Huygens Principle MCQ Quiz in मराठी - Objective Question with Answer for Huygens Principle - मोफत PDF डाउनलोड करा

Concept:

Wavefront:

• It is defined as the locus of all points where the wave has the same phase of the sinusoid.
• The term wavefront is meaningful for fields that, at each point, vary sinusoidally in time with a single temporal frequency.
• Wave Fronts usually move with time
• There are three types of wavefronts plane wavefront, spherical wavefront, and cylindrical wavefront.

Spherical Wavefront:

• When the point source is an isotropic medium, sending out waves in three dimensions, the wavefronts are spheres centered on the source, as shown in the figure.
• Such a wavefront is called a spherical wavefront.

​

Cylindrical wavefronts:

• When the light source is linear, we obtain a cylindrical wavefront.
• In a cylindrical wavefront, all the points equidistant from the linear source lie on the surface of a cylinder, as shown in the figure.

​

Plane wavefront:

• The wavefront will appear as a plane when viewed from a considerable distance from a source of any kind.
• Such a wavefront is called a plane wavefront.

​

Explanation:

• Light emerges from a convex lens when a point source is placed at its focus.
• The shape of the wavefront in case of a light emerging out of a convex lens, when a point source is placed at its focus is a plane.
• 
• The plane wavefront consists of parallel grids.

CONCEPT:

• Huygen's Principle Definition: Every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wave front is a line tangent to all of the wavelets.

Huygen’s Refraction: A straight wave front traveling from one medium to another where its speed is less. The ray bends toward the perpendicular since the wavelets have a lower speed in the second medium.

Here 

θ₁ = angle of incidence

θ₂ = angle of refraction

And from the above figure, we can derive that 

\(\frac{\sin {{\theta }_{1}}}{\sin {{\theta }_{2}}}=\frac{{{v}_{1}}}{{{v}_{2}}}\)

Whereas v = n x λ, thus the above equation can be modified as 

\(\frac{\sin {{\theta }_{1}}}{\sin {{\theta }_{2}}}=\frac{{{v}_{1}}}{{{v}_{2}}}=\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}\)

Explanation:

From the above explanation, we can see that according to Huygens refraction of a plane wave the relation between velocity and wavelength of lightwave after refraction can be expressed as

\(\frac{\sin {{\theta }_{1}}}{\sin {{\theta }_{2}}}=\frac{{{v}_{1}}}{{{v}_{2}}}=\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}\)

Hence we can see that option 2, 3, and 4 are all correct

Additional Information

The above equation is also known as Snell's law of refraction and it is generally given as 

n₁ x sin i = n₂ x sin r

CONCEPT:

• Wavefront: The locus of all particles in a medium, vibrating in the same phase is called waveFront.
• The direction of propagation of light (ray of light) is perpendicular to the waveFront.
• Every point on the given wavefront acts as a source of a new disturbance called secondary wavelets which travel in all directions with the velocity of light in the medium.
• A surface touching these secondary wavelets tangentially in the forward direction at any instant gives the new wavefront at that instant. This is called a secondary wavefront.

EXPLANATION:

• From above it is clear that, a wavefront is an imaginary surface where all particles lying on this vibrate in the same phase. Therefore option 1 is correct.

Explanation: 

Huygen's principle of secondary waves

Huygen's principle states that every point on a wavefront acts as a source of secondary wavelets, which spread out in the forward direction at the same speed as the wave. The new wavefront is the tangent to these secondary wavelets.

This principle is mainly used to obtain the wavefront geometrically by considering the secondary wavelets emanating from different points on the initial wavefront.

∴ The correct answer is option 1: obtain the wave front geometrically.

EXPLANATION:

Cylindrical wave front: When the source of light is linear in shape (e.g. a slit) a cylindrical wave front is produced.

It is because, all the points which are equidistant from the linear source, lie on the surface of a cylinder. 

Hence the correct answer is option 2.

EXPLANATION:

Spherical wave front:

If the light is given by a point source of light, and light travels with equal velocity in all directions,

then a spherical wave front is produced.

Hence the correct answer is option 3.

The correct answer is Option 2: Plane.

Explanation:

Wavefront: A surface over which the phase of the wave is constant.

Types of wavefronts:

Spherical wavefront for point sources close to the observer.

Plane wavefront for distant sources where curvature becomes negligible.

Cylindrical wavefront for line sources.

Explanation:

Huygens' Principle:

According to Huygens' Principle, every point on a wavefront is considered a source of secondary wavelets that spread out with the same speed as the wavefront. The new wavefront is the tangent to these secondary wavelets.

The speed of light in a homogeneous medium is constant, hence the velocities of the primary wavefront and secondary wavelets must be equal.

Given that the propagation occurs in a homogeneous medium:

⇒ According to Huygens' Principle, primary wavefront and secondary wavelets travel at the same speed.

Conclusion:

∴ The correct answer is option 3: Primary wavefront and wavelets are equal.

CONCEPT:

Wavefront:

• The locus of all particles in a medium, vibrating in the same phase is called a wavefront.
• The direction of propagation of the wave is perpendicular to the wavefront.

Wavefronts can be of three types:

1. Spherical wavefront:
   • ​​When light is emerging from a point source, the wavefronts are spherical in shape.
2. Cylindrical wavefront:
   • When the source of light is linear, the wavefronts are cylindrical in shape.
3. Plane wavefront:
   • When the light is coming from a very far-off source, the wavefronts are planar.
   • For a plane wavefront, Amplitude remains constant therefore Intensity remains constant.

EXPLANATION:

• When the light wave travels in a vacuum along the x-axis, its direction of propagation is î.
• Since the direction of propagation of light is perpendicular to the wavefront so the wavefront will be in the plane perpendicular to the î.
• In the given option only plane x = a is perpendicular to the î, so x = a represents the wavefront which is moving along the x-axis.
• Hence, option 1 is correct.

The correct answer is option 1) i.e. Ray of light is perpendicular to the wavefront.

CONCEPT:

• Huygens principle: It states that each point on a wavefront is a source of wavelets, which spread forward with the same speed.
• Wavefront: A wavefront is a surface or a line on which the disturbance at every point has the same phase.
• Wavelets: It is a wave-like oscillation with an amplitude that starts at zero, increases, and then decreases back to zero.

EXPLANATION:

• A wavefront is a locus of all the points in a wave that have the same phase.
• The wavefront forms consecutive concentric circles around the source of light.
• The rays show the direction of propagation of the wave.
• Therefore, the rays of light are always normal/perpendicular to the wavefront.